TDA5140A Datasheet, PDF (14/24 Pages) NXP Semiconductors – Brushless DC motor drive circuit

Philips Semiconductors
Brushless DC motor drive circuit
Product specification
TDA5140A
If the chosen value of CAP-TI is too small oscillations can occur in certain positions of a blocked rotor. If the chosen value is too large, then it
is possible that the motor may run in the reverse direction (synchronously with little torque).
Fig.9 Typical CAP-TI and V_MOT1 voltage waveforms in normal running mode.
Other design aspects
There are other design aspects concerning the application
of the TDA5140A besides the commutation function. They
are:
• Generation of the tacho signal FG
• A built-in interface for a PG sensor
• General purpose operational transconductance
amplifier (OTA)
• Possibilities of motor control
• Reliability.
FG SIGNAL
The FG signal is generated in the TDA5140A by using the
zero-crossing of the motor EMF from the three motor
windings. Every zero-crossing in a (star connected) motor
winding is used to toggle the FG output signal. The FG
frequency is therefore half the commutation frequency.
All transitions indicate the detection of a zero-crossing
(except for PG). The negative-going edges are called FG
pulses because they generate an interrupt in a controlling
microprocessor.
The accuracy of the FG output signal (jitter) is very good.
This accuracy depends on the symmetry of the motor's
electromagnetic construction, which also effects the
satisfactory functioning of the motor itself.
Example: A 3-phase motor with 6 magnetic pole-pairs at
1500 rpm and with a full-wave drive has a commutation
frequency of 25 × 6 × 6 = 900 Hz, and generates a tacho
signal of 450 Hz.
PG SIGNAL
The accuracy of the PG signal in applications such as VCR
must be high (phase information). This accuracy is
obtained by combining the accurate FG signal with the PG
signal by using a wide tolerance external PG sensor. The
external PG signal (PG IN) is only used as an indicator to
select a particular FG pulse. This pulse differs from the
other FG pulses in that it has a short LOW-time of 18 µs
after a HIGH-to-LOW transition. All other FG pulses have
a 50% duty factor (see Fig.10).
For more information also see “application note
EIE/AN 93014”.
April 1994
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